a) Field of the Invention
The present invention relates to a magnetic recording medium used with a hard disk drive or the like for storing information by changing magnetization states and to its manufacture, and more particularly to a magnetic recording medium of low noises and its manufacture suitable for suppressing noises to be generated when information is read from the medium.
b) Description of the Related Art
For low noise magnetic recording of a magnetic recording medium used with a magnetic disk drive, it is desired that the size of each magnetic grain of the magnetic film is a single magnetic domain size or finer and to make magnetic interaction between magnetic grains substantially negligible. The single magnetic domain size is defined by a maximum size of magnetic material allowing the material to generate only a single magnetic dipole.
Conventionally, non-magnetic material is added to magnetic material of a magnetic film of a polycrystal structure, and precipitated on the crystal grain boundaries after the magnetic film is formed in order to isolate each crystal grain. In order to make a crystal grain finer, an underlying layer is made thin and crystallized finer, and a magnetic film is hetero-epitaxially grown on the underlying layer.
With the conventional method, non-magnetic material is required to be precipitated at crystal grain boundaries. However, precipitation is likely to be hindered and in many cases non-magnetic material remains in crystal grains more than a solubility limit. This non-magnetic material contained in crystal grains more than a solubility limit lowers a coercive force of crystal grains. If the underlying layer is made thin, it becomes difficult to obtain crystal orientation with excellent magnetic characteristics.